Active implantable medical devices include a housing that is generally designated as “the generator.” The generator is mechanically and electrically connected to one or more “leads” that bear on them one or more electrodes that contact those tissues to which it is desirable to deliver electrical pulses, e.g., to apply stimulation pacing pulses, and/or to collect (detect) an electrical signal. These tissues include, for example, myocardial, nerve, and muscle tissue.
The French standard NF EN 50077 and its international counterpart ISO 5841-3, Implants for Surgery—Cardiac Pacemakers—Part 3: Low-Profile Connectors (IS-1) for Implantable Pacemakers, defines a normalized connection system standard in the industry, which is identified as “IS-1”. The IS-1 standard ensures interchangeability and compatibility of the leads and generators produced by different manufacturers. In this regard, it should be understood that the present invention is not limited to the particular case of a connection system according to the IS-1 standard, nor even to connection systems applicable to cardiac pacemakers.
Typically, the connection between a lead connector—hereafter more simply referred to as “plug”—and a connector of a generator is made by one or more screws that are tightened by the surgeon using an ad hoc tool (e.g., a screwdriver, possibly equipped with a torque limiter) at the time of implantation of the device and/or the lead. This known screw connection system has several drawbacks. First, in addition to requiring a specific tool for its implementation, this system requires the presence of caps provided with sealed slots through which the tool must pass to prevent the terminals from coming into contact with body fluids after implantation. This requirement for sealing the slots through which the tool passes increases the cost and requires a volume or size of the generator at the connector that is large enough to accommodate the tool.
Second, a screw connection system does not prevent from a screwing oversight, whether from an insufficient screwing or from an overtightening of the screw and damaging the device, by the surgeon.
Third, a screw connection system also introduces significant risks of damage to the silicone plug by the screwdriver with a consequent loss of insulation, of removal or stripping of the screw thread at the time of its use, of binding thereof, or of damage to the head of the screw in case of incorrect insertion of the screwdriver.
From an economic standpoint, the use of a screw system generates certain additional costs (e.g., manufacturing of the screw, threading of inserts) and requires providing with the medical device a special tool (e.g., a screwdriver with torque limiter) for tightening the screw. From an industrial standpoint, the use of a screw connector system requires an operation for inserting and adjusting the position of screws in a predetermined position during the packaging of the device, and of addition of a spot of glue to freeze this position of the screw. From a safety standpoint, the operation of screwing the screw by the physician to secure the plug requires special attention, with an implementation time large enough to make sure that the plug is maintained in the housing, precisely and durably.
Despite these acknowledged drawbacks, the screw connection system is still almost universally used. Indeed, the connectivity standards related to implantable medical devices require (i) minimum retention forces sufficient to prevent accidental disconnection at the time of implantation or during the product lifetime, and (ii) a high-quality and enduring electrical contact (i.e., a very low contact resistance) between the connector plug of the lead and the electrical terminal of the implantable device. These two mechanical and electrical requirements are particularly well satisfied by a conventional screw connection system, despite its many disadvantages.
Various other systems for securing the plug into the housing of the connector head have been proposed to overcome the many difficulties and drawbacks outlined above.
Thus, EP 0890371 A1 and its counterpart U.S. Pat. No. 6,112,120, both assigned to Sorin CRM S.A.S., previously known as ELA Medical, describe separating the electrical contact and mechanical retention functions. The electrical contact is ensured by a spring system exerting a radial pressure against the conductive surface of the plug. The mechanical retention of the plug in the housing is secured by a locking wedge inserted between the body of the plug and the housing wall at the outlet thereof.
Another solution is proposed by EP 0900577 A1 (assigned to Sorin CRM S.A.S., previously known as ELA Medical), which implements a locking system with a retractable spring-loaded eccentric, locally applied against the plug and bearing against it response to an attempted extraction.
These solutions are functionally effective, but they involve relatively complex, and therefore expensive to produce, mechanical systems (e.g., including elements such as a spring, eccentric, and slide). They also require a specific release mechanism for the removal of the plug, typically requiring the use of a special tool for removing the holding or retraction force provided by the eccentric. Finally, they require special precautions to durably ensure the efficient sealing required at the connector.
Other known efforts at alternative connection systems implement deformable elastic elements such as metal blades with one or more orifices through which the plug passes when inserting it into the slot, and exerting a radial point of contact between the edge of the orifice and the surface of the plug.
Thus, U.S. Pat. No. 5,252,090 (Giurtino et al.) proposes to block the plug with an elastically deformable metal piece, extending around the plug in a plane substantially radial to the axis of the plug. Deformable tabs formed in the part produce by stemming an anti-kickback effect, preventing any withdrawal or pulling of the plug once it is inserted in the metal part. For disassembly, the part is extended laterally by two symmetrical ears that, by pinching, deforms the piece enough to remove the tabs of the plug and release it. This device is very effective in terms of mechanical retention. However, unlocking the device requires having two entrances on each side of the part, to ensure a symmetrical pinching, and therefore requires providing two release buttons (one on each side of the head connector).
FR 2 662 310 A (Darby et al.), refers to an elastic clamp whose ends of the two arms are folded against one another and are provided with holes corresponding to the diameter of the plug. The holes are shifted when the clamp is in the free state, and they can be aligned by moving the two arms of the clamp. The plug can then be introduced through the two holes, and be retained in the clamp after release of the force exerted to bring the two arms together. This connection system is very effective in terms of mechanical retention of the plug, but it is not designed to be integrated with a generator. Rather, it is presented to serve as a dispensing connector between several leads, this connector being placed away from the generator.